PROJECT SUMMARY/ABSTRACT Oral cavity squamous cell carcinoma (OCSCC) is a very aggressive and deadly disease with poor survival rates following maximal treatments such as surgery and chemoradiotherapy. The immunosuppressive tumor microenvironment (TME) is a major barrier of response to traditional and immune based therapies with only ~15% of patients with recurrent head and neck cancer responding to immune checkpoint inhibitors. Myeloid cells are; abundant in the TME, key mediators of T cell function, and can influence clinical outcomes both positively and negatively. We seek to understand the contribution of myeloid cells to the immunosuppressive TME and advance strategies to modulate these cells in a favorable way, to enhance OCSCC tumor killing. Our group has developed a novel vaccine treatment platform that can reprogram the intratumoral and peripheral myeloid cell compartment to an anti-tumor state. This platform leverages the use of clinically translatable lipid nanoparticles (NPs), combined with personalized tumor derived mRNA (TDRNA) that simultaneously functions as both a vaccine and an immunomodulating agent. We have demonstrated that TDRNA-NP vaccines have significant anti-tumor activity in OCSCC preclinical models and synergize with immune checkpoint inhibitors. In Aim 1, we will determine the mechanism of TDRNA-NP induced myeloid cell mediated immune responses by investigating vaccine induced myeloid cell proliferation, activation and trafficking in preclinical models of OCSCC. In Aim 2, we will identify the mechanistic role of myeloid cells in the synergy between TDRNA-NP vaccines and immune checkpoint inhibitors in murine models of OCSCC. In Aim 3, we will examine the safety, efficacy and immunogenicity of TDRNA-NPs in client-owned felines with spontaneously occurring oral squamous cell carcinoma. These studies will give us insight into the role of the myeloid cell compartment in OCSCC and advance a promising vaccine technology towards first-in-human clinical trials. The P.I. of this project is a head and neck surgical oncologist and witnesses the daily impact head and neck cancer has on patients and recognizes the need to improve patient care through translational research. She is an active member of the Head and Neck oncology program, is strongly supported by her department, and has a mentoring team comprised of world renowned expert tumor immunologist/translational researchers, and head and neck surgeon-scientists. This mentored training and educational program has been carefully designed with research and career objectives that will allow the P.I. to progress toward becoming an expert head and neck cancer immunologist and translational researcher. In summary, this proposal has significant potential to dramatically impact the lives of patients with OCSCC and will provide substantial training and mentorship for the P.I. to become an independent investigator.